NHMFL Strategic Planning Meeting
UF ‐ Physics
April 24, 2014
1. NHMFL High B/T Facility Growth, Plans (NS)
2. Condensed Matter Theory (Vision, Challenges at High B) (Ingersent)
3. Scanning Probe Microscopy (Biswas)
4. Semiconductor Optics (Stanton)
5. Beyond the Quantum Limit (Maslov)
6. Transverse Thermoelectrics (Hershfield)
7. Materials Processing (Meisel)
8. Biophysics (Meisel)
9. Search for Axions (NS)
NHMFL HIGH B/T FACILITY
Mission: Provide Users with access to high fields (16.5 T max.)
and simultaneously very low temperatures (0.4 to 20 mK)
all in an ultra-quiet environment
UNIQUE B/T
THREE STATIONS for USERS
I. High Cooling Capacity (8 nW)
Bay 3:
B=15/16.5T, Tmin ~ 0.4 mK,
homogeneity 1.6x10-5 /cm,
8 nW  t > 6 wks @ 1 mK
II. Medium Cooling Capacity (1 nW)
Bay 2:
B=8T, Tmin ~ 0.04 mK,
homog. ~ 10-4 /cm
t > 2 wks @ 0.1 mK
III. Fast Turn-around Facility
10 T/10 mK -- fast turnaround
test samples & cell design
 Capabilities
magnetic susceptibility, resistivity,
high sensitivity NMR/NQR to 1100MHz,
ultrasound, transport, heat capacity,
dielectric susceptibility
Time constants can be very long at mK
5/16/2014
Sullivandesign
Strategic Planning
UF 4-24-2014 data acq
 Users
work with staff for optimum
and automated
1
European Microkelvin Collaboration
COMPETITION
(Helsinki, Lancaster, London, ENS-Paris,leiden, Heidelberg)
IoPCS, China (Li Lu)
London
Beijing
2013
2001
5/16/2014
Sullivan Strategic Planning UF 4-24-2014
2
Magnet System: 2 Magnets + Compensation coil
cm
140
130
Heat Switch
120
Zero Field Space
110
Top Load Access
100
90
80
PrNi5
~ nW cooling power
8PrNi5
T Magnet
70
60
50
Compensation coils
Thermal Link
40
30
20
10
0
-10
18/20 T Magnet
15.5/16.5 T (current)
-20
-30
Designed as an integral system
5/16/2014
Sullivan Strategic Planning UF 4-24-2014
3
NHMFL High B/T Facility Growth, Plans
STATS.
Housed in MicroKelvin Building
-- uses two thirds of infrastructure
Four dedicated personnel
2 funded by NHMFL (scientist, postdoc.)
(oversight 4 faculty -- have other grants/projects)
Experiments require very long time ( 6 - 9 months)
must have dedicated on site staff to run user experiments
Typically: 4-6 experiments/yr
2-3 new proposals/yr (last 3 years… 1 new user /yr)
60
No. Pubs/Yr
GROWTH
40
Support
(10k$)
He Use (15k$)
FLAT after 2010
30
in Wm Hall)
(Budget $380k /loaded)
USER Requests/Needs
No. Users /Yr
50
(set-up space and fast-turnaround
1. Higher B, seldom lower T
need high B > 25 T
2. Shorter wait time
--- currently 7 – 9 months
20
10
3. Update aging equipment
0
2006
5/16/2014
2007
2008
2009
2010
Added bay 2
2011
2012
2013
Sullivan Strategic Planning UF 4-24-2014
4
NHMFL High B/T Facility Priority, Long Term

Need for Higher B --- currently limited to 16.5 T
--- work with magnet development group for specially designed
HTC magnet (ultra-quiet environment)
Bedell et al. MRS Bull. 1993
Science Examples:
1. Very low T, high B phase diagram solid 3He
unexplored
2. Spin polarized Fermi fluids
Non-linear dynamics at high B, very low T
not understood (D. Lee et al.)
5/16/2014
Sullivan Strategic Planning UF 4-24-2014
5
New LT Technologies
• Exploit available low temperature environment
–
develop devices operating at low T and thus with very low noise T.
Examples:
pHEMPT RF Ampli TN ~ 0.4 K
(1) RF Amplifiers for enhanced NMR sensitivity (Huan et al.)
(2) Magnetometer readout (AF range, same principle as (1)
(3) Tunnel Diode oscillators (unique low power configuration for very low T app.)
contactless conductivity, magnetic susceptibility
(4) SQUID technologies (need field compensated region).
Needs people & budget (past relied on occasional students)
Need dedicated person
Re-entrant RF cavity VHF NMR
660 MHz, 1.5 mK sample T
5/16/2014
Sullivan Strategic Planning UF 4-24-2014
6
Reducing Queue
Open Bay 1 to NHMFL Users
Need additional staff
--- dedicated Staff Scientist plus Post-Doctoral
$240k annual
Equipment upgrade
(3He pumps, power supplies)
$220k one time
Goal: reduce queue for
access to magnet time
to less than 4 months
5/16/2014
Sullivan Strategic Planning UF 4-24-2014
7
5/16/2014
Sullivan Strategic Planning UF 4-24-2014
8
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James Dufty
Statistical mechanics, non-equilibrium
Selman Hershfield
Electron transport, quantum dots
Peter Hirschfeld
Superconductivity, strong correlations
Kevin Ingersent
Strong correlations, nanophysics
Pradeep Kumar
Magnetism & superconductivity
Dmitrii Maslov
Electron transport theory
Khandker Muttalib
Electron transport/ disorder
Sergei Obukhov
Statistical mechanics of polymers
Christopher Stanton
Ultrafast optics, semiconductors
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Scanning Probe Microscopy in High Magnetic Fields
• SPMs such as Scanning Tunneling Microscopes and Atomic Force Microscopes
are powerful techniques for the study of materials and nanostructures
• Addition of a high magnetic field capability will open heretofore unexplored
avenues such as:
1. The local density of states of superconductors at low temperatures and
high magnetic fields (which could perhaps exceed their upper critical
fields)
2. Magnetic field driven changes in structures of multiferroic materials
such as BiFeO3
3. Surface studies of magnetostrictive materials for device applications
4. Magnetic field driven phase transitions in materials such as charge
ordered oxides and heavy fermion materials
4/25/2014
Amlan Biswas
1
Some areas of interest
Scanning tunneling spectra taken at different temperatures on
BSCCO (Pasupathy et al., Science 320, 196 (2008)).
The transition from SC to normal state can be studied as a
function B as opposed to T with an STM in high magnetic fields
similar to the point contact data on PCCO shown below (Yun et
al., arXiv:0712.1614):
4/25/2014
Piezoelectric force microscopy image of BiFeO3 showing the
polarization domains (Zhao et al., Nature Materials 5, 823
(2006)). Behavior of such domains in high magnetic fields could
reveal critical information about the origin of multiferroism in
BiFeO3 and related materials.
Amlan Biswas
2
Feasibility of project at the NHMFL
• The availability of world leading high magnetic field technology
• Recent developments in high magnetic fields (~30 T) using superconductors
as opposed to resistive magnets
• Existing technology and expertise at the NHMFL on low noise electronics and
low mechanical vibration environments
4/25/2014
Amlan Biswas
3
Feasibility of project at the NHMFL
• Existing scanning probe microscope designs can conform to the requirements
of the new NHMFL magnets e.g. the heart of the SPMs, the coarse approach
mechanism, is usually made of non-magnetic materials such as MACOR and
can be designed to fit the constraints of the magnet boresize.
A 1.5 inch diameter coarse approach
mechanism for a low temperature STM
(http://www.phys.ufl.edu/~amlan/ltstm.ht
ml). Such a mechanism could be reduced
in size to fit the high magnetic field bores.
4/25/2014
Amlan Biswas
4
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DMS = Host Semiconductor + Magnetic Impurities
Examples: CdMnTe (II-VI), InMnAs (III-V)
• DMS Large g-factors Spin Polarized Electrons and Holes Spintronics
X = 0%, B = 20 T
InAs
X = 12%, B = 20 T
InMnAs
Large g-factor comes from
alignment of spins of magnetic
ions.
Mn
B
Exchange interaction of Mn
ions and electrons/holes
#LEDD
enhances spin splitting.
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150
0.8
B fields up to
0.6
150 T.
100
0.4
50
0.2
0
0
•
•
•
•
Transmission
Magnetic Field (T)
200
5
10
15
0.0
Time (μs)
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Simulation of CR Spectra
8-band kp method; Jpd and finite kz effects are included
+ Fermi’s golden rule
e-active
h-active
5.53 μm
15 K
InMnAs
16 K
x=0.006
- Absorption (arb. units)
12 K
18 K
x=0
10.6 μm
52 K
51 K
x=0.006
37 K
28 K
x=0
-150
-100
-50
0
50
100
150
B (T)
High Field CR can be used to investigate small
band splittings and changes with doping.
CR in Graphene
⎛ ∇ e A B ⎞
H = c σ ⋅ ⎜
+
⎟ ⇒ En , ± = ± γ
c ⎠
⎝ i
*
where
γ=
2 c*
l
n
, n = 0,1, 2, B
Unusual results for Graphene:
1.  En ,± n ,
n = 0, 1, 2,......
2.  There is an n=0 Landau
Level.
3.  E B
⎛ Φ n-1,k ⎞
Ψ n ,± ( x , y ) ⎜
⎟
⎝ ± i Φ n ,k ⎠
4.  Get both e-active, and hactive CR.
Experimental Results
Rice and LANL
unanealed
Layla G. Booshehri,†, Charles H. Mielke, Dwight G. Rickel, Scott A.
Crooker, Qi Zhang,† Lei Ren,† Erik H. Hároz,† Avinash Rustagi,# Christopher
J. Stanton,# Zhong Jin,ǁ Zhengzong Sun,ǁ Zheng Yan,ǁ James M. Tour,ǁ,%,^ and
Junichiro Kono*,†,‡
annealed
In the annealed sample, CR is seen
for both e-active and h-active!
Can accurately measure Fermi level
(non-contact).
' $
VB to CB Magneto-absorption
&
0.35
C1
2
H1
6
L1
0
Theory
0.28 0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44
E(eV)
E(eV)
b) theory – (unstrained
a) experiment
Magnetic Field B (T)
Valence Bands
-0.04
Expt.
B (T)
H3
-0.02
Expt.
0.28 0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44
8
H2
0.00
E (eV)
4
6T
Theory
0.30
0.02 0
7.4 T
Absorbtion(a.u.)
E (eV)
Absorbtion(a.u.)
Conduction Bands
C2
0.40
unstrained
2
4
B (T)
6
Santos Group - Oklahoma
8
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44
Energy(eV)
1
0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44
Energy(eV)
' $
&
C1
2
H1
6
L1
0
Theory
0.28 0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44
E(eV)
E(eV)
a) experiment
Magnetic Field B (T)
Valence Bands
-0.04
Expt.
b) theory (strain)
B (T)
H3
-0.02
Expt.
0.28 0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44
8
H2
0.00
E (eV)
4
6T
Theory
0.30
0.02 0
7.4 T
Absorbtion(a.u.)
E (eV)
0.35
conduction band spin-splitting
strained
Absorbtion(a.u.)
Conduction Bands
C2
0.40
VB to CB Magneto-absorption
2
4
B (T)
6
Santos Group - Oklahoma
8
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44
Energy(eV)
1
0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44
Energy(eV)
"%#
OPNMR measures transfer of
electron spin to nuclei.
σ
−
expt.
expt.
σ
+
4.7 T
1.51
theory
1.52
1.53
1.54
1.55
Photon Energy (eV)
lh transitions dominate structure.
OPNMR is sensitive to Spin Polarization.
PCCP, 11, 7031 (2009)
Electron Spin Polarization
P = (n↑ − n↓ ) / (n↑ + n↓ )
theory
4.7 T
OPNMR Signal intensity (a.u.)
Signal depends on the sign of
the polarization.
Hayes Group, Wash. U.
1.56
"$
! "
spin-split valence bands
lh4c4
hh3c3
7T
lh4c4
hh4c4
lh3c3
hh2c2
lh2c2
hh3c3
lh3c3
hh2c2
lh2c2
lh0c0
hh0
c0
α n↑ + n↓
hh1c1
" #"# lh1c1
GaAs
____ abs.
Polarization
P = (n↑ − n↓ ) / (n↑ + n↓ )
OPNMR
Measures polarization
Left circularly polarized absorption at the magnetic field of 7T
Diluted Magnetic Semiconductor
Quantum Dots (QDs)
Radial Position Controlled Doping
of
Semiconductor Quantum Dots
Change magnetism by changing the radial position of the
Mn ion in the dot. This changes the sp-d exchange
interaction between electrons and holes in the dot and the
Mn ions.
Can tune the spin-splitting and g-factors in these materials.
Effective g factors vs Mn Doping Radius
!06# /*-.'5'/ *-E;F)H)%(+5-%/9/*(.
KG>F *-
KE>F *-;
2.2
Mn Doped CdS/ZnS Core/Shell Dot
5
%-0*)
CB
2
1.8
1.6
3
4
2
2
Rc
1
HH,LH
1
1.4
CdS
core
0
FI).$''
4
1
2.0
10
20
ZnS
shell
30
0
40
50
Mn Doping Radius Ri (Angstroms)
Hole g factors
FI*-
Electron g factors
4
Dmitrii MASLOV, UF Theory
Zc
eB
; Rc
mc
vF
Zc
;l
B
hc
eB
Z cW ~ l / Rc
Zc
k
T
B
Classical magnetoresistance, dHvA-ShdH
Z c
2 2
~ kF l B
E
F
Ultra-quantum limit and beyond
LI (phase breaking length)
l
B
Phase-coherent phenomena
Life beyond the (ultra-quantum)
limit:
field-induced phases
Z c
2 2
~ kF l B ! 1
E
F
Europhys. Lett., 55 (3), p. 383 (2001)
Magnetic-field-induced Luttinger liquid
C. Biagini, D. L. Maslov, M. Yu. Reizer, L. I.
Glazman
Abstract
It is shown that a strong magnetic field applied
to a bulk metal induces a Luttinger-liquid
phase. This phase is characterized by the zerobias anomaly in tunneling: the tunneling
conductance scales as a power law of voltage
or temperature. The tunneling exponent
increases with the magnetic field as BlnB.
3D Quantum Hall Effect in Hole-Doped Graphite
Figure
g
2: Dependence
p
of carrier density
y
on Br intercalation time extracted from
Hall (bottom curve) and optical (top
curve). measurements.
Energy levels of bulk graphite (meV) in a 20 T
field along the c-axis
B. Andrei Bernevig, Taylor L. Hughes, Srinivas
Raghu, and Daniel P. Arovas, Phys. Rev. Lett.
99, 146804 (2007)
S. Tongay, J. Hwang, D. B. Tanner, H. K. Pal, D.
Maslov, A. F. Hebard, Phys. Rev B 81, 115428
(2010)
Z cW ~ l / Rc ! 1
Zc
!1
k
T
B
Classical magnetoresistance, dHvA-ShdH
How boring classical
magnetoresistance can be?
U B 1
U 0 1 Z W W v
B 2W T W T 2
c
2
phonons: 1/W v T Ÿ
B 2 / T scaling
Fermi liquids? 1 / W v T
2
Has anyone seen B 2 / T 2 scaling of U?
Non-Fermi liquids Shorter times Ÿ stronger fields!
Wiedemann-Franz law (or its violation):
much better seen for transverse components
Lxy N xy / T V xy
Do we understand the “ tale of two times” in the cuprates?
Uv
cot T
1
W
vT
V xx 1
v
V xy W
Why linear magnetoresistance is so
ubiquitous?
Graphite
Graphene
Topological insulators
…
Why parallel magnetoresistance is so
strong?
I
B
Synopsis: What would Lorentz say?
Necessary and sufficient condition for
longitudinal magnetoresistance
H. K. Pal and D. L. Maslov, Phys. Rev. B 81,
214438 (2010)
Band structure: few % (up to 10%)
Graphite: enormous parallel magnetoresistance (B along I along c-axi
Have we seen any marked deviations
from the Lifshitz-Kosevich formula
near quantum critical points?
LI ~ l
B
Phase coherent phenomena
Have we seen any signatures of phase
coherence in strongly correlated
materials?
Claim: all we know about electron-electron interactions in “good” metals comes from
phase-coherent effects: weak (anti) localization and Altshuler-Aronov effect.
In bad metals, we are still measuring the “Drude” conductivity
LI
DW I v1 / T
Challenge: shorter phase-breaking
lengthsÆ stronger fields
Challenge:
universal conductance fluctuations in
bad metals
What a mesoscopic sample of a bad metal would show?
Challenge:
high-temperature weak localization
Common wisdom: weak localization is a low temperature phenomenon.
Electron –impurity scattering forms a trajectory.
Electron-electron interaction breaks the phase
e WI
GV : ln
h W
2
U
U const: defects
2
5
{AT CT
{
FL
phonons
below TD
U v T : phonons above
the Debye temperature
Classical bosons: N ph ~
T
Z
Scattering on phonons in the classical regime (T ! TD ) is elastic.
Momentum relaxation: fast.
Energy and phase relaxation: slow (energy diffusion).
B.L. Altshuler, A.G. Aronov, D.E. Khmelnitsky,
J. Phys. C 15(36), 7367-7386 (1982).
k BTD
kBT
Typical k of phonons: k ~ kD ~ kF
W ~ T 1
W I ~ T 1/3
2
W
e
2e
T
I
GV : ln ~ ln
3
T
h
W
h
D
2
EF
Quantum magnetoresistance
at high T the same as at low T
LI
DW I ~ l
B
On the absolute scale, LI is short!
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“New Thrusts”: Materials Processing in High Magnetic Fields and Gradients
(comments by Mark Meisel, UF, who did not present any slides at the time
DOE ERFC (Energy Frontier Research Center) Proposal submitted and pening.
“The Center for Extreme Magnetic Field Science”
PI: Ian Baker, Dartmouth College
CoPI: Gerald M. Ludtka,ORNL, and his group has a webpage:
(http://web.ornl.gov/sci/physical_sciences_directorate/mst/mpg/AP_magnetic.shtml
UF Part:
Michele Manuel, UF MSE, http://www.mse.ufl.edu/people/mse-faculty/michele-manuel/
Jennifer Andrew, UF MSE, http://www.mse.ufl.edu/people/mse-faculty/jennifer-andrew/
(Jennifer Andrew was in attendance for this discussion.)
Mark Meisel, UF Physics and NHMFL (only NHMFL person involved as Co-PI)
Comment: “Materials Processing” in US, Japan, and Europe should be considered for
PPHMF-2015 as the next generation of HTC magnets are being planned.
“Biophysics/Bioengineering Discussion
(comments by Mark Meisel, UF, who did not present any slides at the time
UF Physics:
Steve Hagen is only full-time, funded faculty member in biological physics.
http://www.phys.ufl.edu/~hagen/
Steve was in Europe, but his thoughts about thinking beyond the present confines
involved improved central facilities, as communicated by Meisel.
Joanna Long commented that such facilities were located near the AMRIS site.
The issue of having more access to a confocal microscope was picked by
Carlos Rinaldi, UF BME, http://www.bme.ufl.edu/people/rinaldi_carlos , who was present.
Carlos has the idea of adding nonstandard adaptors to a confocal microscopic for
imaging magnetic nanoparticles.
Aslo attending was Jon Dobson, UF BME, http://www.bme.ufl.edu/people/dobson_jon
Ultimately, the point was made that these needs may not be directly related to making
next generation high magnetic fields available to users. However, these points serve as
points of conversation. The conversation involved the microscopy facilities at NHMFL.
Finally, when Alex Angerhofer was describing a nanoliter EPR coil assembly, the point
was made that assembly facilities would be needed by eventual users.
5'#4%*(14#:+105 %1.&&#4-/#66'4
--- High B, Low T, ultra-quiet
Leading question(s) in Astrophysics/Cosmology today:
origin and composition of dark matter and dark energy
Dark Matter -- must be non-baryonic, cold (non-relativistic)
responsible for anomalous rotation curves of matter in galaxies,
motions of galaxy clusters, lensing….
Axions (originally postulated to solve strong CP problem
in strong interactions)
neutron dipole moment
violates P and CP
born cold in early universe, should exist as halos around galaxies, mass ~ 10-1000 PeV
-- possible to detect expected abundance in lab. experiments
Milky Way axions can be detected by Sikivie method:
decay in a strong B field via Primakoff effect to microwave photons
pioneered at UF and BNL, now at Seattle with multi-university collaborations
microwave photon (Detect with high Q microwave cavity)
4/25/2014
strong B
For B = 7T, V = 500 L, m ~ 2 GHz,
all DM=axions, Q ~105
Sullivan Strategic Planning UF 4-24-2014
Power emitted
P ~ 10
-21
W
1
AXION Magnet: Search for Dark Matter
Potential MagLab Involvement
Develop higher-field, larger-volume persistent magnet
Existing Detector at
U. of Wash.
Baffling
Bucking Magnet
SQUID
“1K”Pot
Microwave Cavity
Main Magnet
8 Tesla
600 mm Bore
13 ton
4/25/2014
Sullivan Strategic Planning UF 4-24-2014
ADMX Collaboration Institutions: U. Of Washington, U. of Florida, LLNL, Nat. Radio Astronomy Observ., UC Berkeley, Sheffield U.
2
ADMX, U. Wash, UF, LLNL, Berkeley
Superheterodyne receiver
4/25/2014
Sullivan Strategic Planning UF 4-24-2014
High Q Cu cavity
3
FUTURE
•
•
Need High B2V
B ~ 25 T, V same (500 l), improve sensitivity by factor of 12
must maintain ultra-quiet environment
Lower noise T, current limit is physical T
need to cool with dil fridge (planned 2015 +)
quantum noise limit ~ 50 mK (close J. Clarke et al.)
Solenoids Present & Future, Mark Bird 2014
CICC = Cable-In-Conduit Conductor
SRC = Stabilized Rutherford-Cable
Mono = Monolithic Conductor
Pers = persistent
Ti = NbTi, Sn = Nb3Sn
B 02 V
(T2m3)
B4
(kT4)
Magnet
Application/ Technology
Location
Field
(T)
Bore
(m)
Len
(m)
Energy
(MJ)
Cost
($M)
12000
29
ITER CS
Fusion/Sn CICC
Cadarache
13
2.6
13
6400
>500
5300
0.2
CMS
Detector/Ti SRC
CERN
3.8
6
13
2660
>4581
650
7
Tore Supra
Fusion/Ti Mono Ventilated
Cadarache
9
1.8
3
600
500
160
20 T, 1m
Axion/HTS CIC
?
20
1
2
>600
490
21
ITER CSm
/
Fusion/SnCICC
Cadarache
12
2.6
2
1000
70
~70
430
19
Iseult
MRI/Ti SRC
CEA
11
75
11.75
1
4
338
164
320
29
ITER CSMC
Fusion/Sn CICC
JAEA
13
1.1
2
640
>502
290
3112
60 T out
HF/HTS CICC
MagLab
42
0.4
1.5
1100
250
12
Magnex
MRI/Mono Pers
Minnesota
10.5
0.88
3
286
190
8
M
Magnex
MRI/M
P
MRI/Mono Pers
JJuelich
li h
9
4
9.4
0
9
0.9
3
190
70
41
45 T out
HF/Sn CICC
MagLab
14
0.7
1
100
143
12
2
ADMX
Axion/Ti mono/SRC
U Wash
7
0.5
1.1
14
0.4
0 11
0.11
0
6
0.6
40
15
4/25/2014
5
29
900 mod
Sullivan
UF 4-24-2014
mono Strategic Planning
21 1
NMR/Sn
MagLab
21.1
7.8
4